Surface plasmon resonance (SPR) spectroscopy is a label-free sensing technology that can monitor the thermodynamics and kinetics of biological binding processes, and more generally, real-time changes in the local dielectric environment. It has the potential as a mobile analytical system for the rapid detection of food-borne or environmental pathogens and for health monitoring. The current commercialised SPR systems, however, require external light sources which are not integrated with the sensor. The necessity for external light sources inhibits miniaturisation and mobility of the sensor, and demands precise alignment of the illumination.
A planar, chip-based localised surface plasmon resonance (LSPR) biosensor has been developed wherein a monolayer of gold nanoparticles are immobilised on a glass surface and subsequently functionalised with a biological ligand. Biomolecular binding events are sensed when the functionalised glass coverslip is immersed in a solution containing the target analyte by measurement of a change in surface plasmon absorbance associated with the gold nanoparticles as a result of the change in local refractive index. This method employs an external light source and photodetector. Details of this biosensor can be found in the following publications: Analytical Chemistry, 74, No. 3, 504 (2002); Optics Letters, 25, No. 6, 372 (2000); and U.S. Pat. No. 7,129,096.
There have been various reports [e.g. see Nano Res 2008, 1: 123-128 and Adv. Mater., 16, No. 1, 87 (2004)] of electroluminescence devices employing n-type ZnO nanowires synthesised atop p-type GaN surfaces. Evidence suggests that the nanowires themselves act as waveguides to the light generated at the p-n junction. In the devices reported so far, there are contributions to the electroluminescence spectrum from band-band transitions, acceptor to band transitions in GaN, and defect states. Furthermore, these devices all employ metallic layer top contacts to the ZnO nanowires which are not transparent to the light generated and prevent further functionalisation of the nanowire tips.
US patent application no. US 2007/0140638 A1 describes the application of nanowires and nanoribbons which have diameters lower than the wavelength of light as optical waveguides for the formation of optical circuits and devices. The focus of this document is on the general application of nanowires as waveguides (specifically ZnO and SnO2 nanowires), the coupling of light between adjacent nanowires, and optical sensors based on a single nanowire waveguide integrated with multiple microfluidic channels.
U.S. Pat. No. 7,319,046 B2 describes an integrated optoelectronic silicon biosensor for the detection of biomolecules labelled with chromophore groups or nanoparticles. This biosensor comprises a p-n junction light-emitting diode (LED) light source and a p-n junction LED photodetector, and couples the light between them using a silicon nitride optical waveguide. The waveguide is integrated with a microfluidic channel and interfaces with the biological medium where modulation of the optical coupling takes place.
None of the prior art documents describe a nanoscale LSPR sensor comprising an integrated light source, waveguide and nanoparticle.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present disclosure may or may not address one or more of the background issues.